1. Field of the Invention
The invention relates to an electronically controlled electric motor intended for use in an environment with solvents, with at least one rotor bearing permanent magnets and a stator having coils, in which motor position sensors for ascertaining a commutating-time are arranged in the stator.
2. Description of the Related Art
Such electric motors are often referred to as electronically commutated DC motors and are used, for example, in fuel tanks for driving a fuel pump. If the coils are arranged in the stator, the electric motor does not require any carbon brushes for the transmission of electrical energy. The electric motor is consequently distinguished as an inexpensive drive with a long service life in the lower and medium power ranges. Hall sensors are generally used as position sensors. The Hall sensors have semiconductor chips with terminal contacts. The semiconductor chips and the terminal contacts are usually sheathed in plastic. The disadvantage of the known position sensors is that the semiconductor chips are of a very complex construction due to their sheathing. Furthermore, the semiconductor chips, soldering points of the terminal contacts are not solvent-resistant in the long term. Plastic sheathings also cannot offer adequate protection against the diffusion of solvents, so that, in spite of sheathing, the semiconductor chips are attacked by the solvents. These occurrences of damage to the semiconductor chips mean that the position of the rotor can no longer be reliably sensed by the position sensor.
The invention is based on the problem of designing an electric motor of the type stated at the beginning in such a way that it can be produced as inexpensively as possible and has a very high resistance to solvents.
This problem is solved according to the invention by the position sensors having an electrical conductor which is induced by a moving magnetic field to generate a signal and by the electrical conductor being produced integrally with connecting leads.
This design obviates the need for the position sensor of the electric motor according to the invention to have any sheathing, since an electrical conductor, such as a copper wire for example, is not attacked by solvents. As a result, particularly inexpensive position sensors can be used in the electric motor according to the invention. The integral production of the electrical conductor with the connecting leads also allows the position sensor to be fitted very easily and not to require any solvent-resistant soldering points. The electric motor according to the invention can consequently be produced particularly inexpensively and has a very high resistance to the solvents. A further advantage of this design is that the position sensor can be arranged very close to the magnet of the rotor, so that the position of the rotor can be determined particularly exactly.
The connecting leads of the position sensor could, for example, be screw-connected to continuing leads, to avoid soldering points which are not solvent-resistant. However, the fitting of the electric motor according to the invention is made even easier if the connecting leads of the position sensor are led to a solvent-free space. In the case of the electric motor intended for driving the fuel pump arranged in the fuel tank of a motor vehicle, the connecting leads can consequently be led to outside the fuel tank.
According to another advantageous development of the invention, the position of the rotor can be determined particularly exactly if the electrical conductor is designed as a coil. For this purpose, the coil may be arranged between the phase windings of the stator.
At particularly low rotational speeds of the rotor, the position of the rotor can be easily determined according to another advantageous development of the invention if the electrical conductor is designed as a pulse wire arranged transversely with respect to the movement of the magnet poles of the rotor.
For reasons of space, it is often not possible to arrange the position sensor within the coils of the stator. According to another advantageous development of the invention, the position sensor can be arranged at a position remote from the permanent magnets of the rotor if the rotor has position magnets arranged away from its, permanent magnets and opposite the position sensor. This also makes it possible to avoid a. falsification of the signals of the position sensor due to electric currents flowing in the coils of the stator. Furthermore, it is possible to arrange in the electric motor according to the invention more position magnets than the rotor has permanent magnets. This allows the position of the rotor to be determined particularly exactly.
In a further refinement, a disk which is subdivided into a plurality of regions, the regions being differently magnetized, is arranged instead of the position magnets.